This invention relates to paper handling systems, and more particularly, to a duplex copying system which employs a buffer set means for duplexing.
Duplex copying systems that employed buffer sets of storage means in the past have used a set-stacker, bottom retard feeder and duplex return transport means to achieve the duplex function.
Bottom sheet feed devices have been employed as duplex buffer trays in the past that included pressurized air to reduce friction between the bottom sheet and the sheet stack tray and minimize friction between the bottom sheet and sheets immediately adjacent thereto. In order to prevent mis-feeds, a tri-roller feed belt has been employed having two stationary rolls and a movable roll, the stationary roll disposed beneath the edge of the sheet stack serving to support the feed belt against the lower sheet for feeding the sheet from the stack, the movable roller being disposed adjacent the aforesaid stationary roller for movement into engagement with the bottom sheet of the stack in the event that a sheet is not forwarded at the proper time under the influence of the belt section above the stationary roller. The displacement of the movable roller increases the surface area of the belt in contact with the bottom sheet of the stack to exert a greater feed force thereon.
Problems encountered during the use of such systems included some mis-feeding of sheets which reduced reliability of the systems, and the cost of the buffer feeders for duplex was significant in that stack separators were used with retard feeder mechanisms in addition to numerous other devices in order to make the systems work.
The present invention is intended to overcome the above-mentioned disadvantages and comprises a duplex buffer set means for temporarily storing a set of one-sided copies that are to be subsequently refed from the buffer set means for second sided copying. The buffer set means includes receiving means for receiving sheets with images on one side thereof from a copy processor and for stacking the one-sided sheets in a stacking means. Means are also included for forwarding the sheets out of the stacking means back to the copy processing means for images to be placed on the other side of the sheets. The forwarding means includes shingling means for indexing each sheet out of the stacking means by a predetermined amount coordinated with the arrival of each incoming sheet in said receiving means to form a buffer set of one-sided sheets with each sheet in the set offset from the other sheets by said predetermined amount.